ELECTROPHYSIOLOGY OF HIPPOCAMPAL NEURONS: III. FIRING LEVEL AND TIME CONSTANT

Abstract

An intracellular microelectrode analysis of hippocampal neurons of anesthetized cats has shown that, in the majority of units studied (approx. 75%), impulse initiation occurs upon graded depolarization to a critical level which is constant with different modes of activation. In this respect hippocampal neurons behave in essentially the same way as spinal motoneurons. Estimates of "total" neuron time constant with the use of the strength-latency relationship and the bridge unbalance method give an average value of 9.9 msec. This is significantly longer than that of cat spinal motoneuron. Rheobase for intracellular stimulation of hippocampal neurons is approximately l-5xl0-10A. The value of "total" neuron resistance (RSD) has been roughly estimated from the ratio of firing level to rheobase, and was found to be approximately 13 M[OMEGA].